Figure 4

NEXAFS spectra of Ta\(_\textrm{2}\)NiSe\(_\textrm{5}\) (left), Ta\(_\textrm{2}\)Ni\(_\mathrm {0.93}\)Co\(_\mathrm {0.07}\)Se\(_\textrm{5}\) (middle) and Ta\(_\textrm{2}\)NiS\(_\textrm{5}\) (right) with the beam parallel to a, b, and c directions. Shown is the spectrum taken at 390 K and the difference \(\Delta\)I = I(390 K) - I (T) between the spectra taken at 390 K and at the respective temperatures given in the graph. Note that \(\Delta\)I is multiplied by a factor of -6 and that a negative area means loss of spectral weight relative to 390 K. The green arrows point to the isosbestic point. The insets in the upper left corner of figures (a), (b), and (c) illustrate the polarization of light with respect to the sample’s orientation. A significant charge transfer from orbitals with exclusively in-plane character, i.e., d\(_\textrm{xy}\), to orbitals with in- and out-of-plane character, i.e., d\(_\textrm{yz}\), is found below T\(_C\) for Ta\(_\textrm{2}\)NiSe\(_\textrm{5}\) and Ta\(_\textrm{2}\)Ni\(_\mathrm {0.93}\)Co\(_\mathrm {0.07}\)Se\(_\textrm{5}\), while only a minor charge transfer of this type is found between in-plane and out-of-plane orbitals for Ta\(_\textrm{2}\)NiS\(_\textrm{5}\). For Ta\(_\textrm{2}\)NiS\(_\textrm{5}\), temperature effects seem to play the dominant role..